This invention relates to devices for separating oxygen from a more complex gas containing oxygen to deliver the separated oxygen for use More particularly, the invention relates to solid state electrochemical devices for separating oxygen from a more complex gas
It has been demonstrated that oxygen can be removed from more complex gasses, such as air, by an electrochemical process of ionizing the oxygen molecules transporting the oxygen ions through a solid electrolyte and reforming the oxygen molecules on the opposite electrolyte surface of the electric potential is applied to a suitable catalyzing electrode coating applied to the surface of the electrolyte which is porous to oxygen molecules and which acts to dissociate oxygen molecules into oxygen ions at its interface with the electrolyte. The oxygen ions are transported through the electrolyte to the opposite surface, which is also coated with a catalyzing electrode and electrically charged with the opposite electric potential which removes the excess electrons from the oxygen ions, and the oxygen molecules are reformed.
The material forming the ion conductor, as is known, is a ceramic, and a wide variety of ceramics have been found useful for this purpose. For example, as discussed in U.S. Pat. No. 5,385,874 doped metal oxide ceramics have been found to provide high oxygen ion conductivity. The metal oxide may comprise from about 75% to about 90% of the overall composition, and typical oxides used to form the basis of the compositions may include zirconia, ceria, bismuth oxide, thoria, hafnia and similar materials known in the ceramics art. These are but examples, and the specific selection of material is not a part of the invention described herein.
As discussed, the generation of oxygen from electroded ceramic electrolytes or ion conductors is well knows These principles have been used in a wide variety of structural forms, i.e, the shape of the ceramic electrolyte and the arrangement of electrodes on or within the electrolyte have taken a variety forms. Each of these forms, how ever, has been found to have significant disadvantages in terms of the amount of surface area available for oxygen generation per unit volume and weight, the electrical connections have been difficult to manage, the collection devices for the oxygen output are difficult to manufacture and integrate with the electrolyte and the sources of gas from which oxygen is to be separated often are restricted.
For example, in some of the devices of this type, the ceramic electrolyte is constructed as a large flat plate, and this has significant disadvantages. It is limited in its ability to withstand high output delivery pressures Consequently, the plate must be either thicker, have stiffening ribs or have short spans between the sealed edges all of which add significantly to cost and manufacturing complexity.
U.S. Pat. No. 5,302,258 describes a device where a plurality of tubes each having electrodes on the interior and exterior surfaces thereof, are used The tube design is an improvement in terms of its ability to withstand higher pressures. However, considerable labor cost are are involved for sealing each tube to a manifold and to make the necessary electrical connections to each of the tubes.
U.S. Pat. No. 5,205,990 describes a honeycomb configuration which provides a less expensive way to produce the necessary surface area for the process and is structurally adequate to withstand the higher delivery pressures desirable. The ceramic electrolyte in this configuration has a series of channels, a portion of which are electroded with a first polarity, and the others of which are electroded with a second polarity, these channels are said to form the honeycomb appearance This arrangement has significant disadvantages in the labor required to seal the ends of numerous oxygen collecting channels and the wiring needed to connect those same channels. The alternating rows of oxygen and air channels provide only half the effective surface area as might be available from the amount of ceramic electrolyte used, and the electrical connections throughout this honeycomb structure are intricate and expensive to manufacture.
It is therefore an object of this invention to provide a ceramic oxygen generator having an electrolyte configuration which provides for an increased active surface area per unit volume and weight of ceramic material.
Another object of this invention is to provide a ceramic oxygen generator wherein the electrical connections to the individual anode and cathode surfaces are simplified and less costly to make.
A further object of this invention is to provide a ceramic oxygen generator wherein the manifold structure for receiving the separated oxygen is an integral part of the manufactured generator structure and is less costly to make.
Still another object or this invention is to provide a ceramic oxygen generator which is of a modular configuration and thereby provides a simple "building block" approach to meet differing requirements for amounts of oxygen to be generated.
An additional object of the invention is to provide a ceramic oxygen generator meeting the foregoing objectives which is capable of operating with oxygen containing entrance gasses of a wide variety of pressures.